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        <h1 id="1-虚拟-DOM"><a href="#1-虚拟-DOM" class="headerlink" title="1. 虚拟 DOM"></a>1. 虚拟 DOM</h1><ul>
<li>vdom 是 Vue 和 React 的核心</li>
<li>vdom 比较独立，使用也比较简单</li>
<li>如果面试问到 Vue 和 React 和实现，免不了问 vdom，考察基础能力和自学能力</li>
</ul>
<h2 id="1-1-vdom-是什么？为什么会存在-vdom？"><a href="#1-1-vdom-是什么？为什么会存在-vdom？" class="headerlink" title="1.1. vdom 是什么？为什么会存在 vdom？"></a>1.1. vdom 是什么？为什么会存在 vdom？</h2><h3 id="1-1-1-什么是-vdom"><a href="#1-1-1-什么是-vdom" class="headerlink" title="1.1.1. 什么是 vdom"></a>1.1.1. 什么是 vdom</h3><ul>
<li>virtual dom，虚拟 DOM</li>
<li>用 JS 模拟 DOM 结构</li>
<li>DOM 变化的对比，放在 JS 层来做<ul>
<li>前端的 HTML、CSS、JS 只有 JS 是图灵完备语言</li>
<li>图灵完备语言：能实现各种逻辑的语言，判断、循环、递归，高复杂逻辑的语言</li>
</ul>
</li>
<li>提高重绘性能</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">ul</span> <span class="attr">id</span>=<span class="string">"list"</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">li</span> <span class="attr">class</span>=<span class="string">"item"</span>&gt;</span>Item 1<span class="tag">&lt;/<span class="name">li</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">li</span> <span class="attr">class</span>=<span class="string">"item"</span>&gt;</span>Item 2<span class="tag">&lt;/<span class="name">li</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">ul</span>&gt;</span></span><br></pre></td></tr></table></figure>
<p>用 JS 来模拟上面的 DOM 结构</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line">&#123;</span><br><span class="line">  tag: <span class="string">'ul'</span>,</span><br><span class="line">  attrs: &#123;</span><br><span class="line">    id: <span class="string">'list'</span></span><br><span class="line">  &#125;,</span><br><span class="line">  children: [</span><br><span class="line">    &#123;</span><br><span class="line">      tag: <span class="string">'li'</span>,</span><br><span class="line">      attrs: &#123; <span class="attr">className</span>: <span class="string">'item'</span> &#125;,</span><br><span class="line">      children: [<span class="string">'Item 1'</span>]</span><br><span class="line">    &#125;, &#123;</span><br><span class="line">      tag: <span class="string">'li'</span>,</span><br><span class="line">      attrs: &#123; <span class="attr">className</span>: <span class="string">'item'</span> &#125;,</span><br><span class="line">      children: [<span class="string">'Item 2'</span>]</span><br><span class="line">    &#125;</span><br><span class="line">  ]</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h3 id="1-1-2-设计一个需求场景"><a href="#1-1-2-设计一个需求场景" class="headerlink" title="1.1.2. 设计一个需求场景"></a>1.1.2. 设计一个需求场景</h3><figure class="highlight json"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line">// 1. 将该数据展示成一个表格</span><br><span class="line">// 2， 随便修改一个信息，表格也跟着修改</span><br><span class="line">[</span><br><span class="line">  &#123;</span><br><span class="line">    <span class="attr">"name"</span>: <span class="string">"张三"</span>,</span><br><span class="line">    <span class="attr">"age"</span>: <span class="string">"20"</span>,</span><br><span class="line">    <span class="attr">"address"</span>: <span class="string">"北京"</span></span><br><span class="line">  &#125;,</span><br><span class="line">  &#123;</span><br><span class="line">    <span class="attr">"name"</span>: <span class="string">"李四"</span>,</span><br><span class="line">    <span class="attr">"age"</span>: <span class="string">"21"</span>,</span><br><span class="line">    <span class="attr">"address"</span>: <span class="string">"上海"</span></span><br><span class="line">  &#125;,</span><br><span class="line">  &#123;</span><br><span class="line">    <span class="attr">"name"</span>: <span class="string">"王五"</span>,</span><br><span class="line">    <span class="attr">"age"</span>: <span class="string">"22"</span>,</span><br><span class="line">    <span class="attr">"address"</span>: <span class="string">"广州"</span></span><br><span class="line">  &#125;</span><br><span class="line">]</span><br></pre></td></tr></table></figure>
<h3 id="1-1-3-用-jQuery-实现"><a href="#1-1-3-用-jQuery-实现" class="headerlink" title="1.1.3. 用 jQuery 实现"></a>1.1.3. 用 jQuery 实现</h3><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">"container"</span>&gt;</span><span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">button</span> <span class="attr">id</span>=<span class="string">"btn-change"</span>&gt;</span>change<span class="tag">&lt;/<span class="name">button</span>&gt;</span></span><br><span class="line"></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"jquery.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> data = [</span></span><br><span class="line"><span class="undefined">    &#123;</span></span><br><span class="line"><span class="javascript">      name: <span class="string">'张三'</span>,</span></span><br><span class="line"><span class="javascript">      age: <span class="string">'20'</span>,</span></span><br><span class="line"><span class="javascript">      address: <span class="string">'北京'</span></span></span><br><span class="line"><span class="undefined">    &#125;,</span></span><br><span class="line"><span class="undefined">    &#123;</span></span><br><span class="line"><span class="javascript">      name: <span class="string">'李四'</span>,</span></span><br><span class="line"><span class="javascript">      age: <span class="string">'21'</span>,</span></span><br><span class="line"><span class="javascript">      address: <span class="string">'上海'</span></span></span><br><span class="line"><span class="undefined">    &#125;,</span></span><br><span class="line"><span class="undefined">    &#123;</span></span><br><span class="line"><span class="javascript">      name: <span class="string">'王五'</span>,</span></span><br><span class="line"><span class="javascript">      age: <span class="string">'22'</span>,</span></span><br><span class="line"><span class="javascript">      address: <span class="string">'广州'</span></span></span><br><span class="line"><span class="undefined">    &#125;</span></span><br><span class="line"><span class="undefined">  ]</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">// 渲染函数</span></span></span><br><span class="line"><span class="javascript">  <span class="function"><span class="keyword">function</span> <span class="title">render</span>(<span class="params">data</span>) </span>&#123;</span></span><br><span class="line"><span class="javascript">    <span class="keyword">var</span> $container = $(<span class="string">'#container'</span>)</span></span><br><span class="line"><span class="javascript">    <span class="comment">// 清空容器，重要！！</span></span></span><br><span class="line"><span class="javascript">    $container.html(<span class="string">''</span>)</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">    <span class="comment">// 拼接table</span></span></span><br><span class="line"><span class="javascript">    <span class="keyword">var</span> $table = $(<span class="string">'&lt;table&gt;'</span>)</span></span><br><span class="line"><span class="xml">    $table.append($('<span class="tag">&lt;<span class="name">tr</span>&gt;</span><span class="tag">&lt;<span class="name">td</span>&gt;</span>name<span class="tag">&lt;<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">td</span>&gt;</span>age<span class="tag">&lt;<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">td</span>&gt;</span>address<span class="tag">&lt;<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">tr</span>&gt;</span>'))</span></span><br><span class="line"><span class="javascript">    data.forEach(<span class="function"><span class="params">item</span> =&gt;</span> &#123;</span></span><br><span class="line"><span class="undefined">      $table.append(</span></span><br><span class="line"><span class="javascript">        $(</span></span><br><span class="line"><span class="xml">          '<span class="tag">&lt;<span class="name">tr</span>&gt;</span><span class="tag">&lt;<span class="name">td</span>&gt;</span>' +</span></span><br><span class="line"><span class="undefined">            item.name +</span></span><br><span class="line"><span class="xml">            '<span class="tag">&lt;/<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">td</span>&gt;</span>' +</span></span><br><span class="line"><span class="undefined">            item.age +</span></span><br><span class="line"><span class="xml">            '<span class="tag">&lt;/<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">td</span>&gt;</span>' +</span></span><br><span class="line"><span class="undefined">            item.address +</span></span><br><span class="line"><span class="javascript">            <span class="string">'&lt;/td&gt;/tr&gt;'</span></span></span><br><span class="line"><span class="undefined">        )</span></span><br><span class="line"><span class="undefined">      )</span></span><br><span class="line"><span class="undefined">    &#125;)</span></span><br><span class="line"><span class="javascript">    <span class="comment">// 渲染到页面</span></span></span><br><span class="line"><span class="undefined">    $container.append($table)</span></span><br><span class="line"><span class="undefined">  &#125;</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">// 修改信息</span></span></span><br><span class="line"><span class="javascript">  $(<span class="string">'#btn-change'</span>).click(<span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>&#123;</span></span><br><span class="line"><span class="undefined">    data[1].age = 30</span></span><br><span class="line"><span class="javascript">    data[<span class="number">2</span>].address = <span class="string">'深圳'</span></span></span><br><span class="line"><span class="javascript">    <span class="comment">// re-render 再次渲染</span></span></span><br><span class="line"><span class="undefined">    render(data)</span></span><br><span class="line"><span class="undefined">  &#125;)</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">//页面加载完立刻执行（初次渲染）</span></span></span><br><span class="line"><span class="undefined">  render(data)</span></span><br><span class="line"><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br></pre></td></tr></table></figure>
<p>容器需要清空之后再重新加上 table，操作 DOM</p>
<h3 id="1-1-4-遇到的问题"><a href="#1-1-4-遇到的问题" class="headerlink" title="1.1.4. 遇到的问题"></a>1.1.4. 遇到的问题</h3><ul>
<li>DOM 的操作是非常昂贵的，js 的运行效率高</li>
<li>尽量减少 DOM 操作，而不是推倒重来</li>
<li>项目越复杂，影响就越严重</li>
<li>vdom 即可解决这个问题</li>
</ul>
<h3 id="1-1-5-问题解答"><a href="#1-1-5-问题解答" class="headerlink" title="1.1.5. 问题解答"></a>1.1.5. 问题解答</h3><ul>
<li>virtual DOM，虚拟 DOM</li>
<li>用 JS 模拟 DOM 结构</li>
<li>DOM 操作非常昂贵</li>
<li>将 DOM 对比操作放在 JS 层，提高效率</li>
</ul>
<h2 id="1-2-vdom-如何应用，核心-API-是什么？"><a href="#1-2-vdom-如何应用，核心-API-是什么？" class="headerlink" title="1.2. vdom 如何应用，核心 API 是什么？"></a>1.2. vdom 如何应用，核心 API 是什么？</h2><h3 id="1-2-1-介绍-snabbdom"><a href="#1-2-1-介绍-snabbdom" class="headerlink" title="1.2.1. 介绍 snabbdom"></a>1.2.1. 介绍 snabbdom</h3><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// snabbdom在./snabbdom.js</span></span><br><span class="line"><span class="keyword">var</span> snabbdom = <span class="built_in">require</span>(<span class="string">'snabbdom'</span>)</span><br><span class="line"><span class="comment">// 初始化snabbdom,得到patch。随后,我们可以看到snabbdom设计的精妙之处</span></span><br><span class="line"><span class="keyword">var</span> patch = snabbdom.init([</span><br><span class="line">  <span class="built_in">require</span>(<span class="string">'snabbdom/modules/class'</span>),</span><br><span class="line">  <span class="built_in">require</span>(<span class="string">'snabbdom/modules/props'</span>),</span><br><span class="line">  <span class="built_in">require</span>(<span class="string">'snabbdom/modules/style'</span>),</span><br><span class="line">  <span class="built_in">require</span>(<span class="string">'snabbdom/modules/eventlisteners'</span>)</span><br><span class="line">])</span><br><span class="line"><span class="comment">// h是一个生成vnode的包装函数,factory模式？对生成vnode更精细的包装就是使用jsx</span></span><br><span class="line"><span class="comment">// 在工程里,我们通常使用webpack或者browserify对jsx编译</span></span><br><span class="line"><span class="keyword">var</span> h = <span class="built_in">require</span>(<span class="string">'snabbdom/h'</span>)</span><br><span class="line"><span class="comment">// 构造一个virtual dom,在实际中,我们通常希望一个无状态的vnode</span></span><br><span class="line"><span class="comment">// 并且我们通过state来创造vnode</span></span><br><span class="line"><span class="comment">// react使用具有render方法的对象来作为组件,这个组件可以接受props和state</span></span><br><span class="line"><span class="comment">// 在snabbdom里面,我们同样可以实现类似效果</span></span><br><span class="line"><span class="comment">// function component(state)&#123;return h(...)&#125;</span></span><br><span class="line"><span class="keyword">var</span> vnode =</span><br><span class="line">  h(</span><br><span class="line">    <span class="string">'div#container.two.classes'</span>,</span><br><span class="line">    &#123;<span class="attr">on</span>: &#123;<span class="attr">click</span>: someFn&#125;&#125;,</span><br><span class="line">    [</span><br><span class="line">      h(<span class="string">'span'</span>, &#123;<span class="attr">style</span>: &#123;<span class="attr">fontWeight</span>: <span class="string">'bold'</span>&#125;&#125;, <span class="string">'This is bold'</span>),</span><br><span class="line">      <span class="string">' and this is just normal text'</span>,</span><br><span class="line">      h(<span class="string">'a'</span>, &#123;<span class="attr">props</span>: &#123;<span class="attr">href</span>: <span class="string">'/foo'</span>&#125;&#125;,</span><br><span class="line">      <span class="string">'I\'ll take you places!'</span>)</span><br><span class="line">    ]</span><br><span class="line">  )</span><br><span class="line"><span class="comment">// 得到初始的容器,注意container是一个dom element</span></span><br><span class="line"><span class="keyword">var</span> container = <span class="built_in">document</span>.getElementById(<span class="string">'container'</span>)</span><br><span class="line"><span class="comment">// 将vnode patch到container中</span></span><br><span class="line"><span class="comment">// patch函数会对第一个参数做处理,如果第一个参数不是vnode,那么就把它包装成vnode</span></span><br><span class="line"><span class="comment">// patch过后,vnode发生变化,代表了现在virtual dom的状态</span></span><br><span class="line">patch(container, vnode)</span><br><span class="line"><span class="comment">// 创建一个新的vnode</span></span><br><span class="line"><span class="keyword">var</span> newVnode =</span><br><span class="line">  h(</span><br><span class="line">    <span class="string">'div#container.two.classes'</span>,</span><br><span class="line">    &#123;<span class="attr">on</span>: &#123;<span class="attr">click</span>: anotherEventHandler&#125;&#125;,</span><br><span class="line">    [</span><br><span class="line">      h(<span class="string">'span'</span>, &#123;<span class="attr">style</span>: &#123;<span class="attr">fontWeight</span>: <span class="string">'normal'</span>, <span class="attr">fontStyle</span>: <span class="string">'italics'</span>&#125;&#125;,</span><br><span class="line">      <span class="string">'This is now italics'</span>),</span><br><span class="line">      <span class="string">' and this is still just normal text'</span>,</span><br><span class="line">      h(<span class="string">'a'</span>, &#123;<span class="attr">props</span>: &#123;<span class="attr">href</span>: <span class="string">'/bar'</span>&#125;&#125;, <span class="string">'I\'ll take you places!'</span>)</span><br><span class="line">    ]</span><br><span class="line">  )</span><br><span class="line"><span class="comment">// 将新的vnode patch到vnode上,现在newVnode代表vdom的状态</span></span><br><span class="line">patch(vnode, newVnode</span><br></pre></td></tr></table></figure>
<h3 id="1-2-2-重做之前的-demo"><a href="#1-2-2-重做之前的-demo" class="headerlink" title="1.2.2. 重做之前的 demo"></a>1.2.2. 重做之前的 demo</h3><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">"container"</span>&gt;</span><span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">button</span> <span class="attr">id</span>=<span class="string">"btn-change"</span>&gt;</span>change<span class="tag">&lt;/<span class="name">button</span>&gt;</span></span><br><span class="line"></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"https://cdn.bootcss.com/snabbdom/0.7.0/snabbdom.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"https://cdn.bootcss.com/snabbdom/0.7.0/snabbdom-class.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"https://cdn.bootcss.com/snabbdom/0.7.0/snabbdom-props.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"https://cdn.bootcss.com/snabbdom/0.7.0/snabbdom-style.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"https://cdn.bootcss.com/snabbdom/0.7.0/snabbdom-eventlisteners.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">"https://cdn.bootcss.com/snabbdom/0.7.0/h.js"</span>&gt;</span><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">type</span>=<span class="string">"text/javascript"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> snabbdom = <span class="built_in">window</span>.snabbdom</span></span><br><span class="line"><span class="javascript">  <span class="comment">// 定义关键函数 patch</span></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> patch = snabbdom.init([</span></span><br><span class="line"><span class="undefined">    snabbdom_class,</span></span><br><span class="line"><span class="undefined">    snabbdom_props,</span></span><br><span class="line"><span class="undefined">    snabbdom_style,</span></span><br><span class="line"><span class="undefined">    snabbdom_eventlisteners</span></span><br><span class="line"><span class="undefined">  ])</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">// 定义关键函数 h</span></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> h = snabbdom.h</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">// 原始数据</span></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> data = [</span></span><br><span class="line"><span class="undefined">    &#123;</span></span><br><span class="line"><span class="javascript">      name: <span class="string">'张三'</span>,</span></span><br><span class="line"><span class="javascript">      age: <span class="string">'20'</span>,</span></span><br><span class="line"><span class="javascript">      address: <span class="string">'北京'</span></span></span><br><span class="line"><span class="undefined">    &#125;,</span></span><br><span class="line"><span class="undefined">    &#123;</span></span><br><span class="line"><span class="javascript">      name: <span class="string">'李四'</span>,</span></span><br><span class="line"><span class="javascript">      age: <span class="string">'21'</span>,</span></span><br><span class="line"><span class="javascript">      address: <span class="string">'上海'</span></span></span><br><span class="line"><span class="undefined">    &#125;,</span></span><br><span class="line"><span class="undefined">    &#123;</span></span><br><span class="line"><span class="javascript">      name: <span class="string">'王五'</span>,</span></span><br><span class="line"><span class="javascript">      age: <span class="string">'22'</span>,</span></span><br><span class="line"><span class="javascript">      address: <span class="string">'广州'</span></span></span><br><span class="line"><span class="undefined">    &#125;</span></span><br><span class="line"><span class="undefined">  ]</span></span><br><span class="line"><span class="javascript">  <span class="comment">// 把表头也放在 data 中</span></span></span><br><span class="line"><span class="undefined">  data.unshift(&#123;</span></span><br><span class="line"><span class="javascript">    name: <span class="string">'姓名'</span>,</span></span><br><span class="line"><span class="javascript">    age: <span class="string">'年龄'</span>,</span></span><br><span class="line"><span class="javascript">    address: <span class="string">'地址'</span></span></span><br><span class="line"><span class="undefined">  &#125;)</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> container = <span class="built_in">document</span>.getElementById(<span class="string">'container'</span>)</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">// 渲染函数</span></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> vnode</span></span><br><span class="line"><span class="javascript">  <span class="function"><span class="keyword">function</span> <span class="title">render</span>(<span class="params">data</span>) </span>&#123;</span></span><br><span class="line"><span class="javascript">    <span class="keyword">var</span> newVnode = h(</span></span><br><span class="line"><span class="javascript">      <span class="string">'table'</span>,</span></span><br><span class="line"><span class="undefined">      &#123;&#125;,</span></span><br><span class="line"><span class="javascript">      data.map(<span class="function"><span class="keyword">function</span>(<span class="params">item</span>) </span>&#123;</span></span><br><span class="line"><span class="javascript">        <span class="keyword">var</span> tds = []</span></span><br><span class="line"><span class="javascript">        <span class="keyword">var</span> i</span></span><br><span class="line"><span class="javascript">        <span class="keyword">for</span> (i <span class="keyword">in</span> item) &#123;</span></span><br><span class="line"><span class="javascript">          <span class="keyword">if</span> (item.hasOwnProperty(i)) &#123;</span></span><br><span class="line"><span class="javascript">            tds.push(h(<span class="string">'td'</span>, &#123;&#125;, item[i] + <span class="string">''</span>))</span></span><br><span class="line"><span class="undefined">          &#125;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="javascript">        <span class="keyword">return</span> h(<span class="string">'tr'</span>, &#123;&#125;, tds)</span></span><br><span class="line"><span class="undefined">      &#125;)</span></span><br><span class="line"><span class="undefined">    )</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">    <span class="keyword">if</span> (vnode) &#123;</span></span><br><span class="line"><span class="javascript">      <span class="comment">// re-render</span></span></span><br><span class="line"><span class="undefined">      patch(vnode, newVnode)</span></span><br><span class="line"><span class="javascript">    &#125; <span class="keyword">else</span> &#123;</span></span><br><span class="line"><span class="javascript">      <span class="comment">// 初次渲染</span></span></span><br><span class="line"><span class="undefined">      patch(container, newVnode)</span></span><br><span class="line"><span class="undefined">    &#125;</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">    <span class="comment">// 存储当前的 vnode 结果</span></span></span><br><span class="line"><span class="undefined">    vnode = newVnode</span></span><br><span class="line"><span class="undefined">  &#125;</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="comment">// 初次渲染</span></span></span><br><span class="line"><span class="undefined">  render(data)</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript">  <span class="keyword">var</span> btnChange = <span class="built_in">document</span>.getElementById(<span class="string">'btn-change'</span>)</span></span><br><span class="line"><span class="javascript">  btnChange.addEventListener(<span class="string">'click'</span>, <span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>&#123;</span></span><br><span class="line"><span class="undefined">    data[1].age = 30</span></span><br><span class="line"><span class="javascript">    data[<span class="number">2</span>].address = <span class="string">'深圳'</span></span></span><br><span class="line"><span class="javascript">    <span class="comment">// re-render</span></span></span><br><span class="line"><span class="undefined">    render(data)</span></span><br><span class="line"><span class="undefined">  &#125;)</span></span><br><span class="line"><span class="undefined"></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br></pre></td></tr></table></figure>
<h3 id="1-2-3-核心-API"><a href="#1-2-3-核心-API" class="headerlink" title="1.2.3. 核心 API"></a>1.2.3. 核心 API</h3><ul>
<li>h(‘&lt;标签名&gt;’, {…属性…}, […子元素…])</li>
<li>h(‘&lt;标签名&gt;’, {…属性…}, ‘…’)</li>
<li>patch(container, vnode)</li>
<li>patch(vnode, newVnode)</li>
</ul>
<h3 id="1-2-4-问题解答"><a href="#1-2-4-问题解答" class="headerlink" title="1.2.4. 问题解答"></a>1.2.4. 问题解答</h3><ul>
<li>如何使用？可用 snabbdom 的用法来举例</li>
<li>核心 API：h 函数，patch 函数</li>
</ul>
<h2 id="1-3-介绍一下-diff-算法"><a href="#1-3-介绍一下-diff-算法" class="headerlink" title="1.3. 介绍一下 diff 算法"></a>1.3. 介绍一下 diff 算法</h2><h3 id="1-3-1-什么是-diff-算法"><a href="#1-3-1-什么是-diff-算法" class="headerlink" title="1.3.1. 什么是 diff 算法"></a>1.3.1. 什么是 diff 算法</h3><ul>
<li>Linux 中最基本的 diff 命令能找出两个文本文件之间的异常</li>
<li>git diff xxx 查看修改的内容</li>
</ul>
<h3 id="1-3-2-去繁就简"><a href="#1-3-2-去繁就简" class="headerlink" title="1.3.2. 去繁就简"></a>1.3.2. 去繁就简</h3><ul>
<li>diff 算法非常复杂，实现难度很大，源码量很大</li>
<li>去繁就简，讲明白核心流程，不关心细节</li>
<li>面试官也大多不清楚细节，但是很关心核心流程</li>
<li>去繁就简之后，依然具有很大挑战性，并不简单</li>
</ul>
<h3 id="1-3-3-vdom-为何用-diff-算法"><a href="#1-3-3-vdom-为何用-diff-算法" class="headerlink" title="1.3.3. vdom 为何用 diff 算法"></a>1.3.3. vdom 为何用 diff 算法</h3><ul>
<li>DOM 操作是昂贵的，因此需要尽量减少 DOM 操作</li>
<li>找出本次 DOM 必须更新的节点来更新，其他的不更新</li>
<li>这个“找出”的过程，就需要 diff 算法</li>
</ul>
<h3 id="1-3-4-diff-实现过程"><a href="#1-3-4-diff-实现过程" class="headerlink" title="1.3.4. diff 实现过程"></a>1.3.4. diff 实现过程</h3><ul>
<li>patch(container, vnode)<br>createElement()<br>页面初次加载的时候，直接将 vnode 打包渲染到 container 中</li>
<li>patch(vnode, newVnode)<br>updateChildren()<br>数据改变了，生成新的 vnode，将新的 vnode 和旧的 vnode 进行对比，把差异更新到 vnode 中</li>
</ul>
<h4 id="1-3-4-1-patch-container-vnode"><a href="#1-3-4-1-patch-container-vnode" class="headerlink" title="1.3.4.1. patch(container, vnode)"></a>1.3.4.1. patch(container, vnode)</h4><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">createElement</span>(<span class="params">vnode</span>) </span>&#123;</span><br><span class="line">  <span class="keyword">var</span> tag = vnode.tag <span class="comment">// 'ul'</span></span><br><span class="line">  <span class="keyword">var</span> attrs = vnode.attrs || &#123;&#125;</span><br><span class="line">  <span class="keyword">var</span> children = vnode.children || []</span><br><span class="line">  <span class="keyword">if</span> (!tag) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="literal">null</span></span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 创建真实的 DOM 元素</span></span><br><span class="line">  <span class="keyword">var</span> elem = <span class="built_in">document</span>.createElement(tag)</span><br><span class="line">  <span class="comment">// 属性</span></span><br><span class="line">  <span class="keyword">var</span> attrName</span><br><span class="line">  <span class="keyword">for</span> (attrName <span class="keyword">in</span> attrs) &#123;</span><br><span class="line">    <span class="keyword">if</span> (attrs.hasOwnProperty(attrName)) &#123;</span><br><span class="line">      <span class="comment">// 给 elem 添加属性</span></span><br><span class="line">      elem.setAttribute(attrName, attrs[attrName])</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;</span><br><span class="line">  <span class="comment">// 子元素</span></span><br><span class="line">  children.forEach(<span class="function"><span class="keyword">function</span>(<span class="params">childVnode</span>) </span>&#123;</span><br><span class="line">    <span class="comment">// 给 elem 添加子元素</span></span><br><span class="line">    elem.appendChild(createElement(childVnode)) <span class="comment">// 递归</span></span><br><span class="line">  &#125;)</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 返回真实的 DOM 元素</span></span><br><span class="line">  <span class="keyword">return</span> elem</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h4 id="1-3-4-2-patch-vnode-newVnode"><a href="#1-3-4-2-patch-vnode-newVnode" class="headerlink" title="1.3.4.2. patch(vnode, newVnode)"></a>1.3.4.2. patch(vnode, newVnode)</h4><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">updateChildren</span>(<span class="params">vnode, newVnode</span>) </span>&#123;</span><br><span class="line">  <span class="keyword">var</span> children = vnode.children || []</span><br><span class="line">  <span class="keyword">var</span> newChildren = newVnode.children || []</span><br><span class="line"></span><br><span class="line">  children.forEach(<span class="function"><span class="keyword">function</span>(<span class="params">childVnode, index</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">var</span> newChildVnode = newChildren[index]</span><br><span class="line">    <span class="keyword">if</span> (childVnode.tag === newChildVnode.tag) &#123;</span><br><span class="line">      <span class="comment">// 深层次对比，递归</span></span><br><span class="line">      updateChildren(childVnode, newChildVnode)</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">      <span class="comment">// 替换</span></span><br><span class="line">      replaceNode(childVnode, newChildVnode)</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;)</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">replaceNode</span>(<span class="params">vnode, newVnode</span>) </span>&#123;</span><br><span class="line">  <span class="keyword">var</span> elem = vnode.elem <span class="comment">// 真实的 DOM 节点</span></span><br><span class="line">  <span class="keyword">var</span> newElem = createElement(newVnode)</span><br><span class="line"></span><br><span class="line">  <span class="comment">// 替换</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h3 id="1-3-5-问题解答"><a href="#1-3-5-问题解答" class="headerlink" title="1.3.5. 问题解答"></a>1.3.5. 问题解答</h3><ul>
<li>知道什么是 diff 算法，是 Linux 的基础命令</li>
<li>vdom 中应用 diff 算法是为了找出需要更新的节点</li>
<li>diff 算法的实现：patch(container, vnode)、patch(vnode, newVnode)</li>
<li>核心逻辑：createElement()、updateChildren()</li>
</ul>

      
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